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We consider a conventional α - Ω -dynamo model with meridional circulation that exhibits typical features of the solar dynamo, including a Hale-cycle period of around 20 years and a reasonable shape of the butterfly diagram. With regard to recent ideas of a tidal synchronization of the solar cycle, we complement this model by an additional time-periodic α -term that is localized in the tachocline region. It is shown that amplitudes of some decimeters per second are sufficient for this α -term to become capable of entraining the underlying dynamo. We argue that such amplitudes of α may indeed be realistic, since velocities in the range of m s -1 are reachable, e.g., for tidally excited magneto-Rossby waves., Supplementary Information: The online version contains supplementary material available at 10.1007/s11207-023-02173-y., Competing Interests: Competing interestsThe authors declare no competing interests., (© The Author(s) 2023.)

Since two decades, corneal crosslinking (CXL) has been proposed as the sole therapeutic option to halt progression of keratoconus or other ectatic diseases. CXL aims at stiffening the cornea using a combination of ultraviolet-A light and a chromophore (vitamin B2, riboflavin), and has been proposed in various indications, from progressive ectatic diseases to corneal infection. Despite being in clinical use for many years, many controversies and discrepancies exist towards CXL procedure and its exact role is still under debate. We report an up-to-date review of the state of the art of CXL and describe the basic principles, the different existing CXL techniques reporting basic and clinical evidence, as well as the new perspectives and the possible future developments of the procedure., (Copyright © 2020 Elsevier Masson SAS. All rights reserved.)

We investigate numerically the flow of an electrically conducting fluid in a rapidly rotating spherical shell where the inner boundary spins slightly faster than the outer one. The magnetic field evolves self-consistently from an initial dipolar configuration of weak amplitude, and a toroidal field is produced by winding this poloidal field through the internal differential rotation. First, we characterize the axisymmetric field solutions obtained at long times when the Lorentz force is negligible and the flow follows the steady, purely hydrodynamical solution. We then examine the stability of these solutions, focusing on the regime of large magnetic Reynolds numbers where the field is dominantly toroidal. When the ratio of the azimuthal Alfvén frequency to the rotation frequency exceeds a certain value, a nonaxisymmetric instability develops. We show that the instability properties are compatible with those expected for the magnetorotational instability. Finally, we compare the instability properties with predictions obtained from a local linear stability analysis. The linear analysis agrees well with the numerical simulation results, except in a number of cases where the discrepancies are attributed to shearing effects on the unstable modes.

Standard corneal collagen crosslinking (S-CXL) is a safe, approved procedure, but it may result in severe pain, early vision loss and possible complications, such as infectious or sterile keratitis, in some cases. We describe four cases of sterile infiltrates after uneventful S-CXL for keratoconus, from diagnosis to medical management with six months of follow-up, reporting their pathophysiological features, and comparing our findings with published reports. We discuss various possibilities for diagnosing sterile infiltration more rapidly. In terms of the pathophysiology of sterile infiltrate formation, we separated our patients into two types, one with sterile infiltrate from an antigen reaction and the other with sterile infiltrate due to excessive scarring. Early local steroid treatment resulted in a good visual outcome in our cases., (Copyright © 2019 Elsevier Masson SAS. All rights reserved.)

Purpose: To evaluate and compare epithelial remodeling after standard corneal cross-linking (S-CXL) and iontophoresis-assisted CXL (I-CXL) in eyes with keratoconus by anterior segment optical coherence tomography (AS-OCT)., Methods: In this prospective, observational study, AS-OCT and corneal topography were performed before and 1, 3, and 6 months after surgery. Corneal pachymetry was performed and epithelial and stromal thicknesses (central and 16 points on the 6-mm central zone) and the maximum simulated keratometry value (Kmax) were measured., Results: Two groups of 30 patients (60 eyes total) with progressive keratoconus underwent S-CXL or I-CXL. Before surgery, both groups of patients presented with an irregular epithelial thickness profile. At 6 months postoperatively, localized corneal epithelial thinning was observed in the superior (P = .026), inferior (P = .034), inferonasal (P = .024), and nasal (P = .035) areas at 3 mm and in the superior (P = .039), nasal (P = .043), and inferior (P = .01) areas at 6 mm in the SCXL group. Localized corneal epithelial thinning was observed at 3 (P = .04) and 6 (P = .01) mm in the inferior area in the I-CXL group. No significant stromal changes were observed for either group. Kmax was stable in both groups at 6 months., Conclusions: Significant epithelial remodeling occurs after S-CXL, resulting in a thinner, more regular thickness profile than after I-CXL. Epithelial thickness profile measurements after I-CXL could be used as an adjunctive follow-up tool for monitoring the efficacy of CXL in progressive keratoconus. [J Refract Surg. 2018;34(8):551-558.]., (Copyright 2018, SLACK Incorporated.)

Infectious keratitis are a frequent cause of ocular morbidity. Today, new treatments are necessary to combat the emergence of antibiotic resistant germs. Corneal collagen cross-linking has been suggested to treat corneal infectious (PACK-CXL). Its action would be both antimicrobial and protective for the cornea, increasing its biochemical resistence to proteolytic enzymes. In vivo, PACK-CXL might demonstrate good efficacy against bacterial keratitis, contrary to herpetic keratitis for which it is contraindicated. For fungal or amoebic keratitis, results are uncertain regarding its safety and efficacy. The purpose of this paper is to clarify the use of corneal collagen cross-linking to treat infectious keratitis., (Copyright © 2018 Elsevier Masson SAS. All rights reserved.)

Purpose: Few data are available regarding the optimal treatment of multiple sclerosis (MS)-related uveitis. The aim of this study was to describe clinical features of MS-associated uveitis and determine how MS treatment affects the course of uveitis., Methods: Retrospective, multicenter study. Patients were divided into two groups according to the use (group 2) or not (group 1) of immunomodulatory drugs. Characteristics of uveitis and treatment were reviewed., Results: A total of 68 eyes from 36 patients (17 in group 1 and 19 in group 2) were included. All patients were treated with topical and/or systemic steroids for uveitis. Uveitis occurred 1-17 years prior to neurologic symptoms in 78% of patients. Uveitis was more severe in group 2 (p<0.05), with a tendency toward a higher rate of chronic uveitis (p = 0.06)., Conclusions: MS-related uveitis has often a favorable evolution. Patients on interferon-beta have more severe and chronic uveitis. As far as we are concerned, interferon-beta given on the sole indication of uveitis is not recommended. If steroid-sparing agent is required for intraocular inflammation, immunosuppressive drugs should be considered.

Purpose: To compare the efficacy, safety, and microstructural corneal changes during 2 years after conventional corneal collagen cross-linking (C-CXL) and transepithelial corneal CXL by iontophoresis (I-CXL) for keratoconus., Methods: Eighty eyes of 80 patients with progressive keratoconus were treated by C-CXL (n = 40) or I-CXL (n = 40). Patients were investigated before surgery and 1, 3, 6, 12, and 24 months after treatment. We measured central corneal thickness and maximal simulated keratometry values (Kmax) and performed specular microscopy and in vivo confocal microscopy at each time point. The demarcation line was assessed 1 month after treatment., Results: Kmax remained stable after I-CXL during the entire study period (P = 0.56), whereas the average keratometry increased by 0.2 diopter (50.9 ± 5.6-51.1 ± 5.2). Kmax significantly decreased 1 (P = 0.02) to 2 years (P < 0.01) after C-CXL, with an average decrease of 1.1 diopters (49.9 ± 4.5-48.8 ± 4.2). The failure rate of I-CXL was 20% and that of C-CXL 7.5%. The demarcation line was superficially visible in 35% of cases after I-CXL compared with 95% of cases after C-CXL. Endothelial cell density and central corneal thickness remained stable during the entire study period. The change in Kmax 2 years after C-CXL and I-CXL and the preoperative Kmax were negatively correlated (r = 0.14, P = 0.013, and r = 0.17, P = 0.007, respectively)., Conclusions: I-CXL halted progression of keratoconus less efficiently than did C-CXL after 2 years of follow-up. Longer prospective studies are still needed to ensure I-CXL efficacy.

Keratoconus is a bilateral and progressive corneal ectasia. In order to slow down its progression, corneal collagen cross-linking (CXL) has recently been introduced as an efficient treatment option. In biological and chemical sciences, crosslinking refers to new chemical bonds formed between reactive molecules. Hence, the aim of corneal collagen CXL is to synthetically increase the formation of crosslinks between collagen fibrils in the corneal stroma. Despite the fact that the efficiency of the conventional CXL (C-CXL) protocol has already been shown in several clinical studies, it might benefit from improvements in duration of the procedure and removal of corneal epithelium. Hence, in order to provide a coherent evaluation of two new and optimized CXL protocols, we studied keratoconus patients who had undergone one of the three CXL treatments: iontophoresis (I-CXL), accelerated CXL (A-CXL), and conventional CXL (C-CXL). A-CXL is a 6 time faster CXL procedure using a ten time higher UVA irradiance but still including an epithelium removal. Iontophoresis is a transepithelial non-invasive technique in which a small electric current is applied to improve riboflavin penetration throughout the cornea. Using anterior segment optical coherence tomography (AS OCT) and in vivo confocal microscopy (IVCM), we conclude that regarding the depth of treatment penetration, conventional CXL protocol remains the standard for treating progressive keratoconus. Accelerated CXL seems to be a quick, effective and safe alternative to treat thin corneas. The use of iontophoresis is still being investigated and should be considered with greater caution.

Ultrasonic frequency is a key parameter determining multibubble sonoluminescence (MBSL) spectra of water saturated with Ar/O2 gas mixtures. At 20 kHz, the MBSL is quenched by oxygen. By contrast, at high-frequency ultrasound the maximal MBSL intensity is observed in the presence of Ar/20%O2 gas mixture. Nevertheless, oxygen has no influence on the shape of MBSL spectra. The effect of oxygen on MBSL is explained by oxygen dissociation inside the collapsing bubble which is much more effective at high ultrasonic frequency compared to 20 kHz ultrasound. In contrast to MBSL, a higher yield of H2O2 is observed in Ar/20%O2 gas mixture whatever the ultrasonic frequency. At 20°C and 20% of oxygen the maximal yield of H2O2 is observed at 204-362 kHz. The maximal yield of H2O2 is shifted to 613kHz when the bulk temperature is raised up to 40°C. Coupling of high-frequency ultrasound with mechanical stirring and intensive Ar/O2 bubbling improves H2O2 production. Comparison of MBSL and sonochemistry allowed to conclude that H2O2 is formed from non-excited OH (X(2)Π) and HO2 radicals. Finally, it was shown that at the studied conditions the efficiency of ultrasonic degassing is hardly influenced by frequency., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Corneal collagen crosslinking (CXL) is, at present, the only treatment that can slow or even stop the progression of keratoconus. It uses riboflavin and ultraviolet A (UVA) to create covalent bonds ("crosslinks") between collagen fibrils thus increasing corneal rigidity. Although to date there has been no direct evidence of intrastromal corneal crosslinking, several studies have reported the safety and efficacy of the conventional CXL protocol. This protocol is indicated for progressive keratoconus with a minimal corneal thickness (without the epithelium) of at least 400 μm. It should be performed as early as possible in patients under 18 years with keratoconus or with post-LASIK ectasia. Because of the epithelial debridement, it may rarely induce complications such as infectious keratitis or stromal scars. A variety of new protocols is under investigation and may reduce the rate of these complications. In addition, combination of CXL with other surgical treatments (intracorneal ring segments or photorefractive keratectomy) may improve visual outcomes in patients with keratoconus. Finally, the antimicrobial and anti-edematous properties of CXL have been shown, suggesting new therapeutic indications of this procedure such as infectious keratitis or stromal edema in the future., (Copyright © 2015 Elsevier Masson SAS. All rights reserved.)

Purpose: We compared the efficacy and early morphological changes in the cornea following conventional (C-CXL), transepithelial by iontophoresis (I-CXL), and accelerated (A-CXL) collagen cross-linking in keratoconus., Methods: A total of 45 eyes of 45 patients with progressive keratoconus who underwent corneal collagen crosslinking (CXL) was divided into three groups: C-CXL (n = 15), A-CXL (n = 15), and I-CXL (n = 15). Patients were examined before surgery and at 1-, 3-, and 6-month intervals following surgery. Density of corneal sub-basal nerves, anterior and posterior keratocytes, corneal endothelium, demarcation line depth, and maximal simulated keratometry values (Kmax) were all assessed., Results: Compared to preoperative values, the mean corneal sub-basal nerve and anterior stromal keratocyte densities were significantly lower at 6 months in the C-CXL and A-CXL groups (P < 0.001), whereas they returned to preoperative values in the I-CXL group (P = 0.083 and P = 0.909, respectively). The corneal demarcation line was visible 1 month after surgery in 93% of cases (mean depth, 302.8 ± 74.6 μm) in the C-CXL group, 87.5% (mean depth, 184. 2 ± 38.9 μm) in the A-CXL group, and 47.7% (mean depth, 212 ± 36.5 μm) in the I-CXL group (P = 0.006). There were no significant differences between confocal microscopy and optical coherence tomography measurements of the corneal demarcation line depth (P > 0.05). The Kmax, corneal central thickness, and BSCVA remained stable during the whole study period., Conclusions: Iontophoresis was associated with weaker damage of corneal sub-basal nerves and anterior keratocytes compared to conventional procedures, but the demarcation line was present in less than 50% of cases and was more superficial than with the traditional procedure., (Copyright 2014 The Association for Research in Vision and Ophthalmology, Inc.)

Activation of group III metabotropic glutamate (mGlu) receptors has been recently highlighted as a potential approach in the treatment of Parkinson's disease (PD). This study evaluates the antiparkinsonian action of systemic administration of the broad-spectrum agonist of group III mGlu receptors, 1-aminocyclopentane-1,3,4-tricarboxylic acid (ACPT-I), and investigates its site of action within the basal ganglia circuitry. Acute injection of ACPT-I reverses haloperidol-induced catalepsy, an index of akinesia in rodents. In a rat model of early PD based on partial bilateral nigrostriatal lesions, chronic (2weeks) administration of ACPT-I is required to efficiently alleviate the akinetic deficit evidenced in a reaction time task. This treatment counteracts the post-lesional increases in the gene expression of cytochrome oxidase subunit I, a metabolic marker of neuronal activity, in the overall subthalamic nucleus and in the lateral motor part of the substantia nigra pars reticulata (SNr) but has no effect in the globus pallidus. Paradoxically, ACPT-I administration in sham animals impairs performance and induces overexpression of cytochrome oxidase subunit I mRNA in the lateral SNr, and has no effect in the subthalamic nucleus or globus pallidus. Altogether, our results provide new evidence for the antiparkinsonian efficiency of group III mGlu receptor agonism, point to the regulation of the overactive subthalamo-nigral connection as a main site of action in an early stage of PD and underline the complex interplay between these receptors and the dopaminergic system to regulate basal ganglia function in control and PD conditions., (Copyright © 2012 Elsevier Inc. All rights reserved.)

The thalamic centromedian-parafascicular (CM/Pf) complex, mainly represented by Pf in rodents, is proposed as an interesting target for the neurosurgical treatment of movement disorders, including Parkinson's disease. In this study, we examined the functional impact of subchronic high-frequency stimulation (HFS) of Pf in the 6-hydroxydopamine-lesioned hemiparkinsonian rat model. Pf-HFS had significant anti-akinetic action, evidenced by alleviation of limb use asymmetry (cylinder test). Whereas this anti-akinetic action was moderate, Pf-HFS totally reversed lateralized neglect (corridor task), suggesting potent action on sensorimotor integration. At the cellular level, Pf-HFS partially reversed the dopamine denervation-induced increase in striatal preproenkephalin A mRNA levels, a marker of the neurons of the indirect pathway, without interfering with the markers of the direct pathway (preprotachykinin and preprodynorphin). Pf-HFS totally reversed the lesion-induced changes in the gene expression of cytochrome oxidase subunit I in the subthalamic nucleus, the globus pallidus, and the substantia nigra pars reticulata, and partially in the entopeduncular nucleus. Unlike HFS of the subthalamic nucleus, Pf-HFS did not induce per se dyskinesias and directly, although partially, alleviated L-3,4-dihydroxyphenylalanine (L-DOPA)-induced forelimb dyskinesia. Conversely, L-DOPA treatment negatively interfered with the anti-parkinsonian effect of Pf-HFS. Altogether, these data show that Pf-DBS, by recruiting a large basal ganglia circuitry, provides moderate to strong anti-parkinsonian benefits that might, however, be affected by L-DOPA. The widespread behavioral and cellular outcomes of Pf-HFS evidenced here demonstrate that CM/Pf is an important node for modulating the pathophysiological functioning of basal ganglia and related disorders.

The thalamic centre median-parafascicular complex (CM/Pf), a main input and output station of the basal ganglia, is attracting increasing interest in the field of movement disorders, including Parkinson's disease (PD). CM/Pf undergoes partial neurodegeneration in PD patients and some rodent models. Cellular evidence has been provided in experimental animals that thalamic degeneration may not aggravate but rather counteract the effects of dopamine lesion. But functional changes in the circuits involving the spared neurons could play a detrimental role. This view fits with converging anecdotic and recent direct experience in patients that stress the potential of CM/PF deep brain stimulation (DBS) to alleviate motor disorders, notably tremor and dyskinesias. As a preclinical contribution to the characterization of this target, we investigated the functional impact of CM/Pf-DBS in the 6-hydroxydopamine hemiparkinsonian rat model of PD. When testing different frequencies (25, 60, 130 Hz), only high frequency stimulation (HFS) had significant antiakinetic action as evidenced by alleviation of limb use asymmetry in the cylinder test. Although less efficient than HFS of the subthalamic nucleus in the latter task, CM/PF-HFS completely corrected lateralized neglect in the corridor task. Unlike subthalamic nucleus, CM/Pf-HFS did not induce per se dyskinesias. Finally, the benefits provided by CM/Pf-HFS were associated with widespread impact on the changes in neuronal metabolic activity induced by the dopamine depletion in the basal ganglia. These data point to own particular outcome of CM/Pf-DBS that may be of interest in currently developing multi-target strategies.

We propose a routine protocol based on size fractionation of pelagic samples and the use of the fluorochrome calcofluor white (which binds to beta-1,3 and beta-1,4 polysaccharides) for diagnosing, identifying, and counting chitinaceous fungal parasites (i.e., the sporangia of chytrids) of phytoplankton. The protocol was applied to freshwater samples collected during different seasons (spring and summer/autumn) in two lakes whose trophic statuses varied. Because few samples were collected (i.e., two dates per site), the findings are considered preliminary and mainly a "proof of concept" rather than a valid comparison of sites versus seasons. The results from the proposed protocol indicate higher diversity of infected host and parasite communities than in previous studies. Chytrid epidemics were omnipresent, infecting diverse phytoplankton host communities, primarily diatoms, chlorophytes, and colonial and filamentous cyanobacteria. The diversity and numerical abundance of sporangia and of hosts, and the prevalence of infection (range, <1 to 24% of total host cells) as well, increased from the oligotrophic Lake Pavin to the eutrophic Lake Aydat, while the temporal changes in parasites were apparently more influenced by the host community composition. We conclude that the proposed protocol offers a valid method for the quantitative ecology of chytrid epidemics in aquatic ecosystems and food web dynamics.

There is accumulating evidence that the centre median-parafascicular (CM/Pf) complex of the thalamus is implicated in basal ganglia-related movement disorders and notably in Parkinson's disease. However, the impact of the changes affecting CM/Pf on the pathophysiological functioning of basal ganglia in parkinsonian state remains poorly understood. To address this issue, we have examined the effects of excitotoxic lesion of CM/Pf and of 6-hydroxydopamine-induced lesion of nigral dopamine neurons, separately or in association, on gene expression of markers of neuronal activity in the rat basal ganglia (striatal neuropeptide precursors, GAD67, cytochrome oxidase subunit I) by quantitative in situ hybridization histochemistry. CM/Pf lesion prevented the changes produced by the dopamine denervation in the components of the indirect pathway connecting the striatum to the output structures (striatopallidal neurons, globus pallidus, subthalamic nucleus), and among the output structures, in the entopeduncular nucleus. Preliminary data on the effects of deep brain stimulation of CM/Pf in rats with nigral dopamine lesion show that this surgical approach produces efficient anti-akinetic effect associated with partial reversal of the dopamine lesion-induced increase in striatal preproenkephalin A mRNA levels, a marker of the striatopallidal neurons. These data, which provide substrates for the potential of CM/Pf surgery in the treatment of movement disorders, are discussed in comparison with the effects of lesion or deep brain stimulation of the subthalamic nucleus, the currently preferred target for the surgical treatment of PD.

Abiotic stress is a major limiting factor in crop production. Physiological comparisons between contrasting abiotic stress-tolerant genotypes will improve understanding of stress-tolerant mechanisms. Rice seedlings (S3 stage) of a chilling-tolerant (CT) genotype (CT6748-8-CA-17) and a chilling-sensitive (CS) genotype (INIAP12) were subjected to abiotic stresses including chilling (13/12 degrees C), salt (100mM NaCl), and osmotic (200mM mannitol). Measures of physiological response to the stresses included changes in stress-related sugars, oxidative products and protective enzymes, parameters that could be used as possible markers for selection of improved tolerant varieties. Metabolite analyses showed that the two genotypes responded differently to different stresses. Genotype survival under chilling-stress was as expected, however, CT was more sensitive to salt stress than the CS genotype. The CT genotype was able to maintain membrane integrity better than CS, perhaps by reduction of lipid peroxidation via increased levels of antioxidant enzymes during chilling stress. This genotype accumulated sugars in response to stress, but the accumulation was usually less than in the CS genotype. Chill-stressed CT accumulated galactose and raffinose whereas these saccharides declined in CS. On the other hand, the tolerance mechanism in the more salt- and water-deficit-tolerant CS may be associated with accumulation of osmoprotectants such as glucose, trehalose and mannitol.

The responses of Populus euphratica Oliv. plants to soil water deficit were assessed by analyzing gene expression, protein profiles, and several plant performance criteria to understand the acclimation of plants to soil water deficit. Young, vegetatively propagated plants originating from an arid, saline field site were submitted to a gradually increasing water deficit for 4 weeks in a greenhouse and were allowed to recover for 10 d after full reirrigation. Time-dependent changes and intensity of the perturbations induced in shoot and root growth, xylem anatomy, gas exchange, and water status were recorded. The expression profiles of approximately 6,340 genes and of proteins and metabolites (pigments, soluble carbohydrates, and oxidative compounds) were also recorded in mature leaves and in roots (gene expression only) at four stress levels and after recovery. Drought successively induced shoot growth cessation, stomatal closure, moderate increases in oxidative stress-related compounds, loss of CO2 assimilation, and root growth reduction. These effects were almost fully reversible, indicating that acclimation was dominant over injury. The physiological responses were paralleled by fully reversible transcriptional changes, including only 1.5% of the genes on the array. Protein profiles displayed greater changes than transcript levels. Among the identified proteins for which expressed sequence tags were present on the array, no correlation was found between transcript and protein abundance. Acclimation to water deficit involves the regulation of different networks of genes in roots and shoots. Such diverse requirements for protecting and maintaining the function of different plant organs may render plant engineering or breeding toward improved drought tolerance more complex than previously anticipated.

A mass spectrometer was coupled to high-performance anion-exchange chromatography (HPAEC) with the help of electrochemical neutralization of the eluent and post-column addition of lithium chloride for carbohydrate analysis. Parallel selective channels (single ion monitoring) were used to decrease the detection limits and separate unresolved peaks. The mass specific detection allowed the simultaneous analysis of a wide range of sugar alcohols, mono-, di- and oligosaccharides. Carbohydrates extracted from leaves of poplar submitted to drought stress were analyzed using pulsed amperometric detection (PAD), then mass spectrometry. It allowed the confirmation of peak attribution and the identification of salicin as a major compound in the extracts. Different responses to water deficit and re-hydration were obtained for several carbohydrates, suggesting different roles in osmoprotection processes.

Excess salt in the soil solution affects the plant either through osmotic or ionic effects. Poplar trees, as fast growing pioneer tree species, are thought to be potential suitable candidates for afforestation on saline soils. Osmotic and oxidative stress induced by salinity could be reduced by the production and accumulation of compatible solutes and osmoprotectants in the plant. In this respect, metabolites of this type could be interesting markers for the improvement of salt stress tolerance in breeding programmes. Results have shown that Populus tremula was able to cope with up to 150 mM NaCl without any effect on plant survival. During stress application, the endogenous level of malondialdehyde did not vary significantly between the treatments, indicating that the level of lipid peroxidation was similar in the control and in the stressed plants. However, proline, spermine, sucrose, mannitol, and raffinose levels increased temporarily or throughout the salt treatment. All these molecules are more or less closely related to antioxidant or osmoprotectant mechanisms during stress, suggesting a key role for these compatible solutes, osmoprotectants, and their metabolism for salt stress resistance. The accumulation of free proline, sucrose and mannitol, and the transitory increase in spermine level observable during low and high NaCl application must be considered as general salt stress reaction markers.

In woody plants, chilling stress occurs during the early spring growth and can have important economic consequences. The aim of this study was to compare the reliability of two different experimental systems, 3-month-old softwood cuttings and in vitro-grown shoots, to study chilling effects in a poplar clone (Populus tremula×P. tremuloides cv. Muhs1). Different parameters were recorded: lignin content, sucrose concentration and protein and fresh weight variation, during a 2-week treatment at 10  °C. Two families of polypeptides of high molecular weight (110 and 116 kDa) were shown to accumulate in response to chilling in both cuttings and microshoots. For some of the parameters studied, i.e. appearance of some groups of polypeptides and reduction of fresh weight gain, both in vitro and ex vitro systems were suitable and produced similar results. In contrast, for some other observations, i.e. on sucrose concentration and lignin content, the systems led to different conclusions. While sucrose and lignin contents were shown to increase in cuttings submitted to chilling, no variation in lignin and only a small temporary peak of sucrose could be observed in microshoots kept under chilling. These parameters seem not to be suitable for studying the response of poplar in the in vitro system in such a short-term study.

The extension rate of the first inflorescence node of Arabidopsis was measured during light/dark or continuous light exposure and was found to exhibit oscillations which showed a circadian rhythmicity. Decapitation induced a strong inhibition of stem extension. Subsequent application of IAA restored growth and the associated extension-rate oscillations. In addition, IAA treatments, after decapitation, re-established the circadian rhythmicity visible in the intact plants during free run. This indicates that the upper zone of the inflorescence has a major influence on the extension rate of floral stems and implies a role for auxin. Application of N-(1-naphthyl)phthalamic acid, an IAA transport inhibitor, to an intact floral stem inhibited growth and the rhythmicity in the extension rate oscillations, indicating that IAA polar transport may play a role in the dynamics of stem elongation. Furthermore, IAA-aspartate application, after decapitation, did not restore growth and rhythmicity. Nevertheless, biochemical analysis of IAA and IAA-aspartate demonstrated circadian fluctuations of the endogenous levels of both compounds. These observations suggest that IAA metabolism is an essential factor in the regulation of the circadian growth rhythm of Arabidopsis floral stems.